As one of methods for performing copper plating or bronze plating on steel, there is an immersion plating in which members to be plated are immersed in plating liquid containing copper sulfate or containing copper sulfate and stannous sulphate. This immersion plating utilizes the difference in ionization tendency between iron and copper or stannum, and iron of the amount corresponding to the amount of the plated copper or bronze dissolves in the plating waste liquid.
Because the plating waste liquid contains cations such as Cu ions, Fe ions or the like and ions such as sulfate ions or the like, the plating waste liquid is neutralized and then, metal is recovered therefrom by adding coagulating agent to coagulate the cations, whereby the paling waste liquid thus purified is drained.
Further, as a method for recovering metals from plating waste liquid, there is disclosed a method in which tinning waste liquid containing Fe ions and Sn ions is forced to pass through a strongly acidic cation exchange resin to recover the cations through absorption of the same to the exchange resin and in which then, acid is forced to pass through the exchange resin absorbing the cations to recover the cations in the acid, and Sn is then separated through precipitation (Patent Document 1).